This application claims benefit under 35 USC xc2xa7119 of European patent application No. EP 99125674.4 filed Dec. 22, 1999.
The invention relates to a method and a device for detecting defects in packages, especially in blister packages.
The packages in question are frequently so-called blister packages. A blister package consists of a plastic container, for example of polypropylene (PP) and a cover film, the top of the container being sealed with the film after the moulding has been placed in the plastic container. The films employed are preferably multi-layered films. They consist of a metallic base foil, for example aluminum, a plastic film material mounted thereon, which is printed on the upper side and/or on the side facing the metal foil, and a plastic film material on the lower side, which can be sealed to a plastic container. Laminated foils of this kind are often inscribed on top with various data, such as the use-by date, a batch number and other details describing the contents of the package.
Ophthalmic mouldings are usually put away in a package for storage and for transport. In particular, contact lenses that are produced in large unit numbers, for example disposable contact lenses, are sealed into blister packages. Such contact lenses are preferably manufactured by the so-called mould or full-mould process. In this process, the lenses are manufactured into their final shape between two moulds, so that there is no need to subsequently finish the surfaces of the lenses, nor to finish the edges. The contact lenses produced in this manner are moulded parts having little mechanical stability and a water content of more than 60% by weight. After its manufacture, the lens is metrologically checked and then placed in a blister container, to which isotonic sodium chloride solution (saline) is also added. Then, the cover film is placed on several blister containers, and is sealed to the blister containers by a sealing unit, thus producing a blister strip. The package subsequently undergoes heat sterilisation at 121xc2x0 C. in an autoclave. In order that a single blister package can be separated from the strip again, enabling the customer to open it, the cover film is additionally provided with perforated lines.
Optical components produced in series, e.g. contact lenses, have to be checked for defects such as scratches, shrinkage or edges that have broken away. The components recognised as defective are then rejected. However, at the present time, there is no provision for verifying whether the sealed package has defects. These defects include a defective sealing seam, which for example only makes an incomplete seal or is too narrow, or else cracks in the PP container, so that the isotonic saline can leak out and dry out the contact lens. The customer then discovers an unusable contact lens and is of course annoyed. Or, the contact lens appears to be still usable, but is no longer sterile, since bacteria was able to penetrate into the package through the broken barriers. In addition, the position of the perforations can be shifted when sealing, so that it is only possible to separate a blister package from the blister strip with great difficulty. However, if these defects are recognized by chance or by spot checks, then either the whole batch has to be rejected or all the contact lens packages have to undergo 100% manual checking. Both procedures involve substantial costs. Similar problems also arise with other packages that are filled with sensitive products.
The invention is therefore based on the problem of providing an automatic inspection device with which it is possible to determine, with little effort and without contact, whether packages, particularly sealed blister packages consisting of a blister container and a cover film, are free of defects, especially in respect of the blister containers, the sealing seam and the perforation. Furthermore, the packages recognized as defective should be automatically sorted out. In addition, an inspection device of this kind should enable a high number of units to pass through, since as a rule the goods to be packaged arrive in rapid succession.
The invention solves this problem with the features indicated in claim 1. As far as further essential refinements are concerned, reference is made to the dependent claims.
The invention solves the problem with the use of at least two light sources, which are arranged at a certain distance from one another and each emit a light bundle at a predetermined wavelength range, whereby the emission maxima of the two light sources are offset in relation to one another. The light sources are arranged such that the packages are vertically illuminated. The light reflected by the packages is recorded by a CCD camera and the digital images are stored in a computer, so that they are available in a computer-aided image-processing and documentation system. The images of different packages can be compared with one another, thus making a statistical analysis of defects possible. Moreover, a computer-controlled handling system is provided, which serves to prepare, present and further handle the blister packages. In particular, the damaged blister packages are automatically sorted out.